1. Field of the Invention
The present invention relates generally to waste oil treatment, and more particularly, to an apparatus and process for reclaiming fuel oils from waste oils.
2. Related Art
Waste engine oil and lubricating oil from industry are environmentally hazardous and cause disposal problem. They are collected by public service agency and transferred to commercial station where the oils are reprocessed by centrifugation and filtration and are sold as recycled lubricating oil. Those reprocessed oil is sold for fuel source of boiler as well. The waste oil is frequently subject to thermal cracking process to make #2 diesel fuel.
Lubricating oil is produced when crude oil is subject to a certain boiling range cut of typical 300-500° C. When lubricating oil including synthetic oil performs its job in the engine compartment it usually picks up dirt and heavy metals from the metal parts of engine and from the fuels used. Therefore, typical used oil contains quite substantial amount of cadmium, chromium, zinc and lead. Long period of performance of the oils in the engine helps the lubricating oil go through depolymerization process which results in formation of short hydrocarbons of low boiling point. Procedure of removal of lubricating oil from engine entails clean-up process with solvent, detergent and water etc.
Therefore, a need exists for the development of efficient thermal cracking process to convert the used oil into useful product such as diesel fuel and reduce environmentally hazardous solid and sludge.
U.S. Pat. Nos. 5,286,349 and 5,271,808 disclose an apparatus for reclaiming useful oil products from waste oils. The description of the apparatus basically includes conventional kettle type boiler where some of the boiled material is recovered using a condenser.
FIG. 1 describes a partial diagram showing the conventional thermal cracking apparatus, which is the same as the FIG. 3 of U.S. Pat. No. 5,871,618. Referring to FIG. 1, the cracking apparatus includes a cracking vessel 101 which is comprised of a lid 106, side walls 105, a bottom and a top outlet 120. The conventional apparatus for reclaiming oil product from waste oil is described in U.S. Pat. No. 5,871,618 where open batch type of thermal pot is used at ambient pressure, which is a bit more advanced method than U.S. Pat. Nos. 5,286,349 and 5,271,808 but it still requires long warming up and reaction time. In addition the system requires pause stage for the removal of ash cake every 3.5 days which takes minimum 10 hours as shown in FIG. 2. It should be noticed in the U.S. Pat. No. 5,286,349 that application of heating to the bottom only of the vessel causes formation of sludge cake. In addition it causes different temperature zone from bottom to the top of the waste oil in the vessel, which contributes not only to poor cracking process but also to more formation of sludge cake at the bottom of the vessel.
Accordingly, in the prior art technologies, high-energy requirement, long reaction time, big reactor size and low production rate are unavoidable. Particularly the long reaction time due to large volume of feedstock entails undesirable polymerization, oxidation and dehydrogenation resulting in the production of an unstable diesel fuel and a large volume of sludge cake residues as described in the U.S. Pat. No. 6,132,596. Those shortcomings includes the employment of high temperature up to 450˜500° C. which results in physical damage to the structure of cracking pot, deformation of the structure, high-energy bill and formation of unnecessary by-products such as too short hydrocarbon fragments.